It is known that an internal combustion engine, such a compression-ignition engine (e.g. Diesel) or a spark-ignition engine (e.g. gasoline), operates by cyclically igniting an air/fuel mixture inside the engine cylinders. The combustion of the air/fuel mixture generates hot exhaust gasses, whose expansion causes a reciprocating movement of the engine pistons that are coupled to rotate a crankshaft.
The heat generated by the fuel combustion is partly dissipated by a so called “high-temperature” cooling system, which includes a coolant pump that circulates a coolant, typically a mixture of water and antifreeze, through a plurality of cooling channels realized in the engine block and cylinder head. The coolant exiting from these channels is directed towards a “high-temperature” radiator, where the coolant exchanges the heat received from the engine with the air of the ambient environment, before returning in the coolant pump.
In order to enhance the engine power, the internal combustion engine may be further equipped with a turbocharger, which includes a compressor rotationally coupled to a turbine. The turbine is rotated by the exhaust gasses exiting from the engine cylinders and drives the compressor, which is arranged to increase the pressure of the combustion air directed into the engine cylinders.
Since the compression has the effect of increasing also the air temperature, the air exiting the compressor may be directed into a water-cooled charged-air cooler (WCAC), which is provided for reducing the air temperature before reaching the engine cylinders. To perform this function, the WCAC is usually disposed in a “low-temperature” cooling system, separated from the “high-temperature” cooling system provided for cooling the engine. The “low-temperature” cooling system includes an additional coolant pump that circulates a coolant, typically a mixture of water and antifreeze, through the WCAC first and then through a “low-temperature” radiator provided for reducing the coolant temperature before returning to the coolant pump.
The internal combustion engine may be further equipped with a “long-route” (LR) EGR system (also known as low pressure EGR system), which is provided for recirculating a portion of the exhaust gasses back into the engine cylinders, basically in order to reduce nitrogen oxides (NOx) emissions.
The LR-EGR system usually includes an LR-EGR conduit that branches from an exhaust pipe downstream of the turbine of the turbocharger and leads the exhaust gasses into an intake pipe upstream of the compressor. The LR-EGR system further includes an LR-EGR cooler located in the LR-EGR conduit to reduce the temperature of the exhaust gasses before they reach the intake pipe, and an LR-EGR valve provided for regulating the amount of recirculated exhaust gasses.
The LR-EGR cooler is conventionally disposed in the “high-temperature” cooling system, so that the exhaust gasses flowing through the “long-route” EGR system are cooled by the same coolant that has been used to reduce the engine temperature. Due to this arrangement, the temperature of the coolant entering the LR-EGR cooler may normally be of 90° C. or more, which implies that the LR-EGR cooler needs to be chosen and/or dimensioned to have a good thermal efficiency for these relatively high coolant temperature values.
However, during the warm-up phase of the internal combustion engine, the temperature of the coolant in the “high-temperature” cooling system may be much lower, for example of about 20° C. or less. In these conditions, the efficiency of the LR-EGR cooler results extremely intensified and the exhaust gasses are thus subjected to an extremely severe cooling, which may cause the condensation of the vapor contained in the exhaust gasses into water droplets. When reaching the intake pipe, these water droplets are accelerated by the intake air stream and projected at high speed to collide with the wheel of the compressor.
To prevent the potential damages caused by these collisions, the LR-EGR system may include a bypass valve that, during the engine warm-up, deviates the exhaust gasses coming from the exhaust pipe into a secondary conduit that bypasses the LR-EGR cooler. However, this solution generally complicates and increases the cost of the LR-EGR system and may not guarantee the total absence of condensation. As an alternative, the LR-EGR valve may be controlled to minimize as much as possible the recirculation of the exhaust gasses during the engine warm-up phases. However, this solution represents an important limitation to the functionality of the LR-EGR system, which contributes to increase the pollutant emissions of the engine in those operating phases.
In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.